1. Technical Field of Invention
This invention relates to a method of tuning an alert device in a portable communication apparatus. The invention also relates to a portable communication apparatus having a microphone, an alert device and a controller.
2. Background Art
Portable communication apparatuses, such as mobile telephones, are used in different environments and places having different types of conditions as regards, for example, loudness. If a mobile telephone is used in a very noisy environment the volume of the ring signal must be held at a high level. Still it can be difficult to hear the ring signal, and this problem can be solved with a vibrator, which is frequently used in mobile telephones.
The vibrator is initially set to vibrate at a certain desired frequency, and a driver, which drives the vibrator, is designed accordingly. Due to variations in efficiency of the motor of the vibrators and/or the response and the impedance in the output terminal of the drivers, the actual frequency of the vibrator is seldom the same as the desired frequency. The variations can be +/−50% and more. There is also a drift in the actual frequency due to ageing effects.
If the actual frequency gets too low, the signal gets too weak to be easily noticed by the user of the communication apparatus. When this occurs depends on the design of the communication apparatus and where in the apparatus the vibrator is located. Weight and mounting of the vibrators are the most decisive factors. If the actual frequency gets to high, friction in the vibrator becomes a problem and the vibrator produces too much heat, which has a bad effect on the power consumption of the apparatus, and the wearing and therefore aging of the vibrator also increase. A too high frequency also draws an unnecessary amount of power. Usually, one desired frequency is set, which should not be surpassed.
It is known to measure vibrating frequencies of vibrators by using vibration sensors, such as piezo crystals, rotation sensors and optical sensors. After the measurement of its vibrating frequency, the vibrator can be tuned to a desired frequency. A disadvantage with this solution is that it requires extra components. This means that the cost increases. If the measuring components are integrated with the apparatus having the vibrator, the extra components require extra space which is expensive.
Still another possible solution is to use a laser microphone to measure the vibrating frequency. A disadvantage by using such a laser microphone is that it is very expensive.
U.S. Pat. No. 5,293,161 to Motorola describes how the vibration frequency can be monitored and kept constant. The frequency of the vibrator can be varied by varying a frequency selector. The frequency selector comprises a micro computer programmed via conventional techniques to measure a parameter, such as the amplitude of the actual vibration, of the vibrator. Optionally, the micro computer may monitor a signal such as the current or the voltage of the power supply of the vibrator, or the electromagnetic force of the vibrator. This information is then used to keep the frequency of the vibrator essentially constant or at the desired frequency settings. A disadvantage with this technique is that it requires extra components. The extra components require extra space which is expensive.
As vibrators are finding use in more and more applications, such as a response to some user action, as part of a tactile feedback scheme, as part of a game, as a communication method (such as Morse code) or as a rhythmic element in music, this greater use leads to increased wearing of the vibrator.